Method of treating tubes



April 19, 1932. w. L. KRAHL. 1,854,376

' METHOD OF TREATING TUBES Filed Jan. 27, 1928 INVENTOR www@ ATTORNEY 1;rise to howls, squeals Patented Apr. 19, 1932 "WALTER LOUIS KRAI-L, OFMONTCLAIR, NEW JERSEY, ASSIGNGR TO ARCTUR'US RADIO TUBE COM'FANY, OFNEWARK, NEW JERSEY, A CORPORATON OF DELAWARE METHOD F TREATING TUBESApplication led January 27, 1928. Serial No. 249,904.

This invention relates to vacuum tubes and especially to a method oftreatingl the tube whereby more efficient operation is obtained.

in the manufacture of vacuum 'tubes and especially tubes using carbonfilaments l have found that during the process of exhausting the tube, athin film of material is deposited upon the inner` surface of thcenvelope and also upon the elements and the stein or press of the tube,which hlm apparently comprises particles of carbon, nichel and othermaterial thrown off from the elements during` exhausti n. On the insideof the envelope such a film does no damage but at the stem adjacent theconductors and also the glass bead i, ed to support the upper ends ofthe eler its the presence of this film causes a leali-4 age betweencertain conductors which may result in poor operation of the tube,giving other noises detrimental. to the operation of the tu ie.

Vlfhe object of the invention, therefore, is to provide a. method forbreaking down this thin film of material and eliminating the danger ofleakage be ween the conductors cent the glass.

The invention is illustrated in the accompa-nying` drawing` in which thesingle ligure shows a vacuum tube connected in a circuit to perform themethod of the invention.

The invention may be applicable to any form of vacuum tube but l haveillustrated the vacuum tube shown and described in the apnlication oflf/Valter Louis Krahl entitlet i 'auf v ttmllllll *l During the processof exhausting the tube, a

film l5 is formed upon the stem adjacent the conductors and a film i7also forms upon the glass bead l5. These lms may often be substantiallyinvisible to the naked eye but present a conducting' path which permitscurrent to leal: between the Various conductors.

ln order to eliminate this danger of leakage between the conductors, lhave found that the film may be burned off by introducing high tensioncurrent to the terminals of the tube. Accordingly, an ordinary sparkcoil 18 having a primary winding 19 connected to a source 2O of currentsupply has its secondary winding' 2l connected to any two of theterminals of the tube. Upon the operation of the coil, high tensioncurrent is introduced into the tube through the termi nals and sparksacross the surface of the glass both at the stem 13 and at the bead 15between the conductors, effectively removing the film therefrom. A fewseconds is suiiicient to completely remove the film and the tube nnaythen be shifted so that another set of 'terminals are connected to thehigh tension leads when the current is again turned on.

t will be evident from the above that I have provided an extremelysimple method of removing` the conducting film deposited upon the glassinsulation parts of the tube between the conduct rs which method is easyto carry out and greatly improves the tube so that the efiiciencythereof is increased.

Vilhile l have explained the invention as adaptable to a. treatment of aspecific type of thermionic vacuum tubes, it is to be understood thatyhe invent-ion may be used in connection with any vacuum tubes in whicha deleterious film may be formed in the course of construction orotherwise, between the conduct-ors of the elements. l do not, therefore,desire to limit my invention except as defined in the appended claims.

Having thus described my invention, what l claim is:

l. The method of reducing leakage between conductors in a vacuum tubewhich comprises causing high tension current to flow between saidconductors.

2. The method of reducing leakage between the conductors of a vacuumtube which coniprises applying high tension current to two of saidconductors and thereafter applying high tension current to the remainingconductors in pairs.

In testimony whereof, I aiX my signature.

VALTER LOUIS KRAHL.

